The present invention relates to a control system for a superhigh pressure generation circuit which generates a superhigh hydraulic fluid pressure and maintains the fluid pressure at a preselected level.
In rolling blanks of iron and steel or those of nonferrous materials such as aluminum and copper, it is a prerequisite that the rolling mill processes a blank to a uniform thickness. However, a blank tends to become thicker in a laterally intermediate portion than the rest due to an inherent construction of a rolling mill. A rolling load is applied to a blank from bearing sections at opposite ends of upper and lower rolls with the result that the axes of the upper and lower rollers are bend away from each other with the maximum distance defined substantially at a midpoint between the bearings. Such a tendency is particularly pronounced in a cold rolling mill which exerts a very heavy rolling load onto blanks. The resultant uneven thickness distribution over the width of a blank significantly degrades the quality of a product.
An expedient to establish a uniform inter-roll linear pressure by compensating for the curvatures of the roll axes is disclosed in Japanese Patent Publication No. 46-43978. This prior art expedient employs sleeves or crowns coupled individually around upper and lower rolls and feeds high pressure hydraulic fluid to between each roll and crown, so that the opposite crowns become bulged toward each other in their intermediate portions between the bearings.
For the variable crowns to be so deformed, the rolling mill has to be supplied with a fluid pressure as high as about 500 kg/cm.sup.2 at the maximum, for example. Use of an ordinary hydraulic circuit for the generation of such a high pressure is impractical, however, unless all the components thereof such as a hydraulic pump for generating a fluid pressure, a relief valve for controlling the fluid pressure to a given level, an accumulator for temporary accumulation of the fluid pressure, pipings for induction of the fluid pressure and a check valve for checking reverse flows are designed to fully withstand the high pressure. This obstructs the use of existing industrial hydraulic instruments and requires very expensive parts for exclusive use.
Meanwhile, after a desired high pressure has been reached, a major part of delivery from the high pressure pump is relieved. This brings about another problem that a substantial load necessary for driving such a high pressure pump accompanies a significant loss in the driving energy.
Additionally, the accuracy in the control on the high pressure is limited due to uneven characteristic distributions among relief valves.